1. Field of the Invention
The present invention relates to an image forming apparatus such as copier, printer, facsimile, etc. capable of forming images and repetitively erasing toner images formed on paper, in particular, an image forming apparatus and an image forming method that define amounts of toners adhered on a photosensitive drum.
2. Description of the Related Art
In recent years, a large volume of paper is consumed with the increase of various informational data according to the development of the office automation. On the other hand, sheets of paper are recycled so far for the purpose of saving of paper resources. For example, in the paper recycle, recycled paper is manufactured by processing used sheets of paper with toner image data formed thereon using a voluminous amount of bleaching agent and water. As a result, in the paper recycling, cost of recycled paper is increased and economical efficiency of the paper recycle is impaired and a new environmental pollution may be produced as a result of the processing of waste solution used in the recycling of used paper.
In view of the above, a practical application is attempted to reuse once used paper by erasing image data printed thereon for printing new image data output repeatedly instead of recycling paper by recycling used paper itself in recent years. For reusing used paper, an image is formed or erased using decolorizing toner by cutting off the connection of toner pigment with coupler fixed on paper by heating and the same paper is used repeatedly. When this reused paper is used repetitively, the paper quality will be deteriorated.
So, an image forming apparatus equipped with a toner adhering amount detecting means for detecting amount of toner adhering on a transfer paper is so far disclosed in the Japanese Patent Application Publication No. 7-20666. This conventional image forming apparatus controls the image forming process on a transfer paper according to a toner adhering amount on a reused transfer paper or discards a reused transfer paper.
However, this conventional image forming apparatus is able to control the image forming process by recognizing a characteristic change in the history of reused transfer paper. However, it does not control developing density of decolorizing toner at the time when an image was formed; that is, amount of decolorizing toner adhering to the photosensitive drum.
On the other hand, if the density of a toner image transferred on a paper and fixed thereon was high, the toner decolorization for reusing paper becomes worse. If the density of an image left on a paper after decolorizing toner became to more than 0.2, a previous image not erased and remained becomes conspicuous and a newly printed data will become difficult to read when new data is printed.
So, an image forming apparatus and an image forming method for forming images in good toner decolorizing property after fixed and making it possible to read a newly printed image satisfactorily when forming images using reuse paper are demanded.